Patent GB-649825-A (GB)
Title: Improvements in or relating to signalling systems using coded pulses
IPC: H03M1/00
Filed: 1948-02-27
Abstract: 649,825. Multiplex pulse code signalling. WESTERN ELECTRIC CO., Inc. Feb. 27, 1948, No. 6067. Convention date, May 10, 1945. [Class 40 (v)] Binary pulse code groups of "on " or " off " pulses are generated in accordance with the phases of a plurality of wave sources of difference frequency at the time of occurrence of time modulated pulses. The code groups are reconverted to time modulated pulses at a receiver, by causing the character of the pulses to select a particular phase of a corresponding plurality of waves for connection to an output circuit which contains pulse generating means responsive when all the waves are at a maximum. An eight-channel multiplex communication system is described, the pulse groups in each channel comprising a six-unit code. Transmitter, Figs. 3, 7 and 8.-The transmitter operations are controlled by a stable master oscillator 321 through synchronized square wave multivibrators 325 ... 330, operating at 768, 384, 192, 96, 48 and 24 Kc/s. respectively and 322 ... 324 all operating at 8 Kc/s. but giving the phase-displaced asymmetric outputs 1518 ... 1520, Fig. 15, respectively. The multivibrators 327 ... 330 each have two output waves 1510, 1511... 1516, 1517 of opposite phase, indicated by + and -, Fig. 3. The six pulse storage circuits 712-1 ... 712-6 for one channel of the system are fed with the signal from source 710 after conversion to time modulated pulses in modulator 711 the latter being operated to produce a pulse during one third of the complete multiplex cycle by connection over lead 750 to multivibrator 322. Channels 1, 4 and 7 are controlled in this way by multivibrator 322, channels 2, 5 and 8 by 323 and channels 3 and 6 by 324. The pulse produced during this interval is applied through resistances 728 to the control grids of the storage circuit valves 720-1 ... 720-6. The suppressor grids of these valves are fed from the positive outputs 1313, 1315, 1317, 1319, 1321, 1323, Fig. 13, of multivibrators 325 ... 330 respectively and the valves become conducting to discharge storage condensers 727-1 ... 727-6 if the signal pulse coincides with a positive-going portion of the respective multivibrator wave. Thus, for example, if the pulse is time modulated to position 1311, that is it corresponds to signal amplitude 33, condensers 721-1 ... 721-5 will be discharged and condenser 721-6 will remain charged. The charging time constant is such that the condensers require the whole multiplex cycle to become fully recharged. The sequence of code pulses corresponding to the code elements thus stored is produced by the pulse selecting circuits 813-1 ... 813-6. The control grids of the valves 810 of these circuits are connected to the condensers 727-1 ... 727-6 respectively 'while their suppressor grids are supplied with different combinations of the outputs from multivibrators 327 ... 330 and one of the multivibrators 322 ... 324, through decoupling circuits 729, 730. These combinations are so arranged that, for example, as shown the suppressor grids are energized in succession, for channel 1, in the intervals' 17 ... 22 of a 48-pulse multiplex cycle. The other channels each use six other consecutive intervals. The valves thus become capable of conducting in succession at times when all the applied multivibrator waves are simultaneously positive and those valves emit a pulse which are connected to those of condensers 727-1 ... 727-6 which remain charged. The output pulses control a common video amplifier 310 to which is also applied the output of a pulse generator 320 synchronized by the master oscillator 321, so that amplified and correctlyshaped code pulses are fed to the radio transmitter 311. Receiver, Figs. 4, 8 and 9.-The incoming code pulses from the radio receiver 411 pass to the video amplifier 410 and thence through a phase control 420 to synchronize a 384 Kc/s. oscillator 421. The latter controls the receiver operations through synchronized square-wave multivibrators 425 ... 430, operating at 768, 384, 192, 96, 48 and 24 Kc/s. respectively and 422 ... 424 all operating at 8 Kc/s. in the same manner as circuits 322 ... 324 at the transmitter. The incoming pulses are also fed in parallel to the suppressor grids of valves 820-1 ... 820-6 of pulse storage circuits 814-1 ... 814-6, shown for channel 1 only. These are activated in turn like the pulse selecting circuits 813-1 ... 813-6 at the transmitter and store the code pulses individually on condensers 823-1 under the control of selected multivibrator outputs applied to the control grids of the valves 820-1 ... 820-6. The condition of condensers 823-1 will thus be a replica of the condition of the transmitter storage condensers 727-1 ... 727- 6. The storage condensers are connected to the left-hand control grids of the double pentode clippers 920-1 ... 920-6 in the pulse decoding circuits 913-1 ... 913-6. Each of these circuits has a pair of alternative output valves 931-1, 932-21, &c. which are supplied respectively with the positive and negative outputs of multivibrators 425 ... 430 respectively. Thus, depending on the charged or discharged condition of the corresponding storage condenser, one or other of the output valves feeds the selected multivibrator wave to the common output connected to clipper circuit 912. For the code example quoted above, the circuits 913-1 ... 913-5 will give the positive outputs from multivibrators 425... 429 and circuit 913-6 will give the negative output from multivibrator 430. The only pulse interval during which all these ouput waves are positive is the thirty-third of the sixty-four possible so that clipper 912, which is set to produce an output only when this condition obtains, passes on to the pulse time demodulator 911, a pulse whose timing corresponds with that of pulse 1311, Fig. 13, which was fed to the pulse coding circuits at the transmitter. The demodulator is controlled by a connection from multivibrator 422 so that only the correct output pulse is selected for the channel in question, and supplies the reproducer 910 with the decoded and demodulated signal.